This application is related to Japanese Patent Application No. 10-362585 filed on Dec. 21, 1998, the entire contents of which are incorporated by reference.
1. Field of the Invention
The present invention relates to an illumination system suitable for emitting illumination light to a light modulator, which modulates light according to image information, and to a projector that projects and magnifies the light from the illumination system modulated by the light modulator.
2. Discussion of the Background
FIG. 10 illustrates a background projector. A light beam emitted from a light source passes through a uniform illumination optical system 20 and is separated into three color light beams of red (R), green (G), and blue (B) by a non-illustrated color separation optical system. The three color light beams are respectively modulated according to image information by liquid crystal panels 51 for the respective colors (R, G, and B). The modulated three color light beams are synthesized to a composite light beam by means of a prism 61. The composite light beam is projected through a projection lens 71 onto a screen S for projection of a magnified image.
The uniform illumination optical system 20 includes a first lens array 21, a second lens array 22, and a condenser lens 23. The light beam emitted from the light source 10 is divided into a plurality of partial light beams by the first lens array 21. The partial light beams are superimposed on the liquid crystal panel 51 by the second lens array 22 and the condenser lens 23. Namely, the uniform illumination optical system 20 has a function of leveling the intensity of the light beams, with which the liquid crystal panel 51 is irradiated.
The optical characteristics of the liquid crystal panel 51 significantly depend upon the angle of the incident light ray. In the background projector using the uniform illumination optical system 20, the rays entering the liquid crystal panel 51 have a large angular difference (hereinafter this angular difference is referred to as the xe2x80x98entrance angle xcex8xe2x80x99), which causes problems like chrominance nonuniformities of the projected image and lowered contrast.
There is a high possibility that the light ray having a large incident angle to the liquid crystal panel 51 can not enter the pupil of the projection lens and might reduce brightness of the projected image.
Accordingly, one object of the present invention is to provide an illumination system and a projector, which reduce the chrominance nonuniformities of a projected image and enhance the contrast, so as to give a bright projected image of high quality.
To achieve the above-noted and other objects, the present invention provides a first apparatus, which is an illumination system that illuminates a modulation device modulating light according to image information. The illumination system includes a light source that emits a light beam along a light source optical axis, a first lens array having a plurality of small lenses which divide the light beam emitted from the light source into a plurality of partial light beams, and a superimposing lens that superimposes the plurality of partial light beams emitted from the first lens array on the modulation device such that light intensity distribution is substantially uniform on the modulation device. Also included is an entrance angle reducing system disposed between the superimposing lens and the modulation device. The entrance angle reducing system reduces an entrance angle of light rays, which are emitted from the superimposing lens and enter the modulation device, compared with an illumination system without the entrance angle reducing system.
The illumination system of the present invention including the entrance angle reducing system reduces the entrance angle of the incident light rays that enter the modulation device. This arrangement effectively reduces the chrominance nonuniformities of an image reproduced by the beams emitted from the modulation device, and improves the contrast.
In the illumination system, it is preferable the superimposing lens and the entrance angle reducing system form a telephoto lens system which causes light rays entering the superimposing lens substantially in parallel with the light source optical axis to be converged on the modulation device. This arrangement facilitates the reduction of the entrance angle of the incident light rays that enter the modulation device.
In the illumination system discussed above, the entrance angle reducing system may include a concave lens or a meniscus lens. The concave lens or the meniscus lens forms in combination with the superimposing lens the telephoto lens system, thereby facilitating the reduction of the entrance angle.
The entrance angle reducing system may also include a convex mirror. The convex mirror used as the entrance angle reducing system also desirably reduces the entrance angle of the incident light rays that enter the modulation device. In the case where the illumination system includes a reflecting mirror that bends the optical path, the convex mirror also functions as the reflecting mirror. This arrangement thus favorably reduces the total number of parts.
In the illumination system, the superimposing lens may include a second lens array, having a plurality of small lenses corresponding to the small lenses of the first lens array. The second lens array may also include decentered small lenses.
The second array including the decentered small lenses functions as the superimposing lens. In the illumination system having a condenser lens as the superimposing lens, the use of the second lens array as the superimposing lens enables reduction of the thickness of the condenser lens and thereby of the weight of the illumination system.
In the illumination system, the light source may include a reflector having a parabolic reflecting surface. The reflector emits the light beam that travels while being converged along the light source optical axis. The superimposing lens may include a second lens array having a plurality of small lenses corresponding to the small lenses of the first lens array. Each small lens included in the second lens array may have dimensions smaller than the corresponding small lens in the first lens array. This arrangement desirably reduces the size of the illumination system.
In the illumination system discussed above, the light beam from the superimposing lens may be emitted to be converged as a whole, whereas the light beam from the entrance angle reducing system may be emitted to be a bundle of parallel light as a whole.
A second apparatus of the present invention is a projector including a light source that emits a light beam along a light source optical axis, a color separator that separates the light beam emitted from the light source into three color light beams, and first through third modulation devices that respectively modulate the three color light beams separated by the color separator according to image information. Also included is a color synthesizer that synthesizes beams modulated by the first through third modulation devices to a composite light beam, and a projection lens that projects and magnifies the composite light beam synthesized by the color synthesizer. The projector further includes a first lens array having a plurality of small lenses which divide the light beam emitted from the light source into a plurality of partial light beams, a superimposing lens that superimposes the plurality of partial light beams emitted from the first lens array on the first through third modulation devices such that light intensity distribution is substantially uniform on the first through third modulation devices, and an entrance angle reducing system disposed between the superimposing lens and the first through third modulation devices. The entrance angle reducing system reduces an entrance angle of light rays, which are emitted from the superimposing lens and enter the first through third modulation devices, compared with an illumination system without the entrance angle reducing system.
The projector of the present invention utilizes the illumination system similar to the first apparatus of the present invention, thereby reducing the entrance angle of the incident light rays that enter the first through the third modulation devices. This arrangement desirably reduces the chrominance nonuniformities of a projected and displayed image and improves the contrast.
In the projector, the color separator may have a first color separator that separates the light beam emitted from the light source into a first color light beam and a residual color light beam, and a second color separator that separates the residual color light beam into a second color light beam and a third color light beam. The entrance angle reducing system may have a first entrance angle reduction element that is disposed in an optical path of the first color light beam separated by the first color separator, and a second entrance angle reduction element that is disposed in an optical path of the residual color light beam separated by the first color separator.
The entrance angle reducing system, which includes a plurality of entrance angle reduction elements, also effectively reduces the entrance angle of the incident light rays that enter the first through the third modulation devices. In the projector, each of the modulation devices may be a liquid crystal panel, which includes a microlens array.
The angular difference of rays emitted from the liquid crystal panel, which includes the microlens array, is generally greater than the entrance angle of the incident light rays that enter the liquid crystal panel. The projector of the present invention has the entrance angle reducing system and thereby relatively reduces the angular difference of the rays emitted from the liquid crystal panel. This arrangement effectively prevents the brightness of the projected image from being lowered.
A third apparatus of the present invention is a projector, which includes an illumination system, a modulation device that modulates light emitted from the illumination system according to image information, and a projection lens that projects and magnifies the modulated light emitted from the modulation device. The illumination system includes a light source that emits a light beam along a light source optical axis, a first lens array having a plurality of small lenses which divide the light beam emitted from the light source into a plurality of partial light beams, a superimposing lens that superimposes the plurality of partial light beams emitted from the first lens array on the modulation device such that light intensity distribution is substantially uniform on the modulation device, and an entrance angle reducing system disposed between the superimposing lens and the modulation device. The entrance angle reducing system reduces an entrance angle of light rays, which are emitted from the superimposing lens and enter the modulation device, compared with an illumination system without the entrance angle reducing system. This projector has the similar functions and advantages to those of the projector discussed previously as the second apparatus of the present invention.